What is gypsum retarder?
Table of Contents
What is gypsum retarder?
Gypsum retarder is an important additive of building materials. Commercial gypsum retarders are mainly composed of four types: organic acids, phosphates, protein and composite retarder. Protein based retarders prolong the setting time of hemihydrates with less strength loss and higher costs.
What are the 4 properties of gypsum products?
Table 2
| S. No. | Brand | W/P ratio |
|---|---|---|
| 6 | Lion | 0.50 |
| 0.55 | ||
| 7 | SNC | 0.45 |
| 0.50 |
What are retarders and accelerators in dentistry?
Modifiers (Accelerators and Retarders) Modifiers are chemicals added in order to alter some of the properties and make it more acceptable to the dentist. If the chemical added, it decreases the setting time, it is called an accelerator, whereas if it increases the setting time, it is called a retarder.
How do you control the time of gypsum?
A material often used to prolong the setting time is 1‒2% borax. Borax can form a coating on a hemihydrate molecule so that it cannot contact water, decreasing the solubility of the hemihydrate (i.e., increasing the setting time). The material often used to speed up setting time is 2‒3% potassium sulfate.
What does plaster retarder do?
Extratime is a chemical additive for use with finishing plasters. The additive slows the curing process of the plaster by slowing the chemical crystal formation that causes the gypsum plaster to set or harden.
Is calcium chloride an accelerator or retarder?
The most widely used accelerator is calcium chloride, which almost all commercially manufactured accelerators contain. The variety of retarders is greater; lignosulfonates and their derivatives, carbohydrates, hydroxy-carboxilic acids, dicarboxilic acids, phosphates and borates are generally used.
What is the composition of gypsum?
Gypsum is calcium sulfate (CaSO4). Refined gypsum in the anhydrite form (no water) is 29.4 percent calcium (Ca) and 23.5 percent sulfur (S). Usually, gypsum has water associated in the molecular structure (CaSO4·2H2O) and is approximately 23.3 percent Ca and 18.5 percent S (plaster of paris).
What is a retarder in dentistry?
(rē-tăr′dĕr) A biomaterial used in dentistry to slow the rate at which impression materials gel, set, or polymerize.
What is setting expansion of gypsum?
Dental gypsum products when mixed with water and allowed to “set” in air exhibit an. expansion of their peripheral boundaries that is known as “normal setting expansion.” When additional water is brought into contact withthe setting material, an increased. expansion is observed.
What is plaster retarder made of?
The usual types of retarders hitherto used for this purpose have been partially hydrolyzed animal or vegetable protein obtained by treating the raw protein material with a hydrolyzing agent, usually sodium hydroxide, whereupon the resulting product was mixed with a carrying medium, which in most cases was ordinary lime …
How do you use plaster retarder?
Pack of 10 single use sachets of plaster retarder, used to extend the setting time for all types of finishing plaster. Simply mix with water, then add plaster powder to extend the setting time for up to 60 minutes, ideal for plastering larger areas or for working in hot environments.